High-Temperature Ultrahigh-Resolution Absorption Cross Section Measurements of O2 in the 91.1-91.8 nm Region

The NII 108.5 nm, NII 91.7 nm, and the OII 83.4 nm are the prominent emission in the EUV airglow. The atmospheric extinction due to absorption by molecular N2 and O2 strongly affects the observed airglow emission fluxes. Since the temperature of the upper atmosphere of the Earth can be as high as 900 K it is important to know all relevant molecular cross sections at such temperatures. Therefore, the high-temperature ultrahigh-resolution photoabsorption cross section measurements of N2 and O2 in the extreme ultraviolet (EUV) region are important to their atmospheric modeling implications. A temperature change on a gaseous sample clearly will affect the Doppler broadened linewidth and the rotational and vibrational population distributions of the ground electronic state from which absorption takes places. The consequences of such a change are the enhancement or elimination of hot bands, the broadening or sharpening of rovibronic line shapes, the decreasing or increasing in cross section values of an absorption feature. In this poster we report ultrahigh resolution absorption cross section measurements of O2 with a resolution of 0.0008 nm in the 91.1-91.8 nm region at temperatures of 535 K and 295 K. The 6.65-m vertical off-plane Eagle spectrometer available at the Photon Factory, KEK, Tsukuba, Japan, was employed in the present study. The detailed temperature-dependent results of this work will be presented. This work is supported by NSF grant ATM-0096761.